title: Differential effects of intranasal insulin and caffeine on cerebral blood flow.
abstract: Insulin is an important modulator of brain functions such as memory and appetite regulation. Besides the effect on neuronal activity, it is also possible that insulin has a direct vasodilatory effect on cerebral blood flow (CBF). We investigated the impact of increased insulin levels in the central nervous system on basal and task-induced CBF as well as blood oxygenation level-dependent (BOLD) response in the visual cortex using pulsed arterial spin-labeling MRI. An intranasal insulin application was used to avoid peripheral hyperinsulinaemia, which would lead to a cascade of hormonal changes. In a control experiment, caffeine was applied due to its well-known impact on the vasculature of the brain leading to a reliable reduction of CBF. Eight lean subjects were included in the study. On 2 separate days, intranasal human insulin or caffeine tablets were given to the subjects after fasting over night. On each day, basal CBF and task-induced CBF were measured before and 30 min after application of insulin or caffeine in each subject. During the task condition, a flickering checkerboard was presented. Insulin had no effect on basal CBF and task-induced CBF in comparison with drug-free baseline measurement in the visual cortex and control regions. After caffeine application, however, there was a significant decrease of CBF during stimulation in the visual cortex. The BOLD response was not altered by insulin or caffeine between pre- and postdose measurements. In conclusion, we found no evidence for a direct vasodilatory effect of intranasal insulin on the cerebral vascular system in this study.
authors.affiliation: Department of Internal Medicine IV, University Hospital, Tübingen, Germany.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Grichisch
authors.forename: Mustafa
authors.initials: M
authors.lastname: Çavuşoğlu
authors.forename: Hubert
authors.initials: H
authors.lastname: Preissl
authors.forename: Kamil
authors.initials: K
authors.lastname: Uludağ
authors.forename: Manfred
authors.initials: M
authors.lastname: Hallschmid
authors.forename: Niels
authors.initials: N
authors.lastname: Birbaumer
authors.forename: Hans U
authors.initials: HU
authors.lastname: Häring
authors.forename: Andreas
authors.initials: A
authors.lastname: Fritsche
authors.forename: Ralf
authors.initials: R
authors.lastname: Veit
mesh_terms: D000281:Administration, Intranasal; D000293:Adolescent; D000328:Adult; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D002560:Cerebrovascular Circulation / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D008279:Magnetic Resonance Imaging; D008297:Male; D014793:Visual Cortex / Q000098:blood supply* / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
chemical_list: D007328:Insulin; D002110:Caffeine